All motor vehicles include a control for switching between high beam and low beam operation of the motor vehicle headlamps. This control may be implemented by a floor mounted switch but most typically in more recent designed motor vehicles is implemented with a stalk on the vehicle steering column that is easily actuated by a motor vehicle operator.
When the high beam option is selected, the vehicle headlamps are focused in a direction that illuminates further in advance of the vehicle to improve a motorist's ability to see details in his or her line of sight. When an oncoming vehicle approaches, the motorist can switch to low beam operation to avoid temporarily blinding the oncoming driver. Fog lamps are occasionally installed on vehicles to direct a lamp output downward in a direction closer to the vehicle to enable the motorist to more clearly see during rain and foggy conditions.
Vehicle head lamps most typically contain two separate light bulbs that can be independently activated. When one of the bulbs is activated, a low beam lamp output is produced and when a second bulb of the two bulbs is activated a high beam lamp output is provided. In the 1980's when headlamps having halogen light bulbs were first built, the government enacted photometric tests. These tests dictated that light of a high enough intensity to cause spot blindness in other motorists did not reach certain regions in a space in front of a motor vehicle headlamp. Spot blindness was only a problem for halogen lights since these lights produce a much more intense output when compared with non-halogen lamps.
U.S. Pat. No. 5,517,389 to Meyers concerns an electrochromic lamp assembly including a reflector having two or more reflective surfaces. A light source and an electrochromic means is positioned between the light source and at least one reflective surface. Each reflective surface directs light in a different direction. The electrochromic means is capable of blocking light from exiting the lamp assembly from at least one direction.
U.S. Pat. No. 5,988,837 to Eichhorn et al. discusses a method for adjusting a vehicle headlight during cornering by superimposing a light distribution pattern with a greater horizontal dispersion than that of a low-bam light onto the low-beam light distribution pattern. Further, fog-light distribution pattern is superimposed onto a low beam light distribution pattern by superimposing the fog-light distribution pattern onto the low-beam light distribution pattern, cornering light with improved laterial illmination is achieved in an uncomplicated manner. A single headlight is used for generating the cornering light by a signal from a sensor which is utilized by an electronic drive for controlling an electric motor so that changes in the cornering light distribution pattern are countered by pivoting a reflector.
FIGS. 1a and 1b show a rear-projection headlamp according to the prior art. A light source 601 is positioned in a headlamp housing 603. A focusing lens 605 is positioned in the housing 603 such that it maximizes the light output of from the light source. A metal stamping 607 is positioned in the housing 603 between the light source 601 and the lens 605. The housing also includes a clear lens cover 609 which covers and protects the lens 605. The internal portion 611 of the housing 603 is coated with a reflective material that reflects light emitted from the light source through the lens 605 and out of the headlamp to an illumination zone. The stamping 607 is used to block unwanted light from being emitted from the light source 601. The light blocked is that which if allowed to exit the headlamp would continue to an upper light field blinding oncoming motorists. The stamping 607 is located at the bottom of the headlamp assembly due to the fact that the lens 605 inverts the light field emitted from the light source 601 as reflected by the reflective coating on the internal portion 609 of the housing 603. This prior art method meets the horizontal cutoff and other photometric test points by utilization of the stamping structure. The drawback to this method is that the lamp is not utilizing the light blocked by the stamping causing decrease light output for any give light source. Therefore, there is a need in the art for a headlamp assembly which can make use of this light thus increasing light output while still meeting the horizontal cutoff and photometric test points.